Filters for fluids (liquids and gases) have been known in the art. For instance, filters are commonly used in such systems as air filtration systems, water filtration systems, water purification systems, etc. One particular application of filters is in recreational waters, such as pools and spas.
At least two types of filters are known. The first type of filter is a cartridge-type filter with a replaceable filter typically mounted on a core and placed in the filtration system. The replaceable filter is typically formed from a porous, relatively soft material having pores sized to prevent contaminants and/or other particles (hereinafter “contaminants” for the sake of convenience, without intent to limit) from flowing through the filtration system, while letting the fluid pass therethrough. However, contaminants and particles typically become embedded in such filters such that the filters must be replaced on a regular basis.
The second type of filter is a Diatomaceous Earth (“DE”) filter having a support grid resembling a nylon mesh on which a powder is deposited. The powder forms a uniform cake-like structure that performs the filtration operation. However, the support grid is relatively fragile and has a limited life. Moreover, such a support grid system assembly is complex and thus relatively difficult to assemble.
Typically, cartridge-type filters are cylindrical elements having a substantially open longitudinal center portion with radially-outwardly extending, longitudinal folded portions or pleats. A plurality of pleats are commonly arranged around a tubular core defining a cylinder. When viewed in a transverse cross-section, the pleats typically extend radially outward from the core toward the outer periphery of the filter. Conventional pleats extend in a straight manner from the inner diameter of the filter (the core) toward the outer diameter (the periphery) of the filter. A drawback of the straight pleat is that, because the filter industry has become standardized, the overall dimensions of the filter body are restricted and a straight pleat cannot be increased in size beyond the dimension of the filter body. Thus the filter capacity and effectiveness are limited.
Because the effectiveness of the standard cartridge-type filter is generally a function of the surface area of the filter, pleats have been modified to extend from the center core toward the periphery in an arched manner. Thus, the effective length of each pleat between an inner diameter and outer diameter can be increased. The increase in the length of each pleat results in an increased surface area of the filter.
In standard cartridge-type filters, to increase the effectiveness of a typical filter, the volume of empty space within the filter body has traditionally been targeted as wasted space. Attempts have been made to approach filling 100% of the volume of the filter body, between the open center core and the periphery, with filter material. Furthermore, the curvature of each pleat between an ascending and descending arm of the pleat has been modified to decrease empty volume at the distal and proximal ends of each respective pleat. The pleats were also designed to contact one another such that minimal empty volume exists between two adjacent pleats. Adjacent pleats often lie directly on neighboring pleats such that adjacent pleats are in intimate contact with each other. The curvature of pleats is typically modified such that the empty volume of the overall filter is reduced to nearly zero.
However, several drawbacks of the traditional system exist. Because the pleats are in intimate contact, any large particles that enter the filter have no particular position in which to become positioned or trapped. The large particles therefore become lodged in unpredicted and unwanted positions and can create dead spaces, disrupting proper functioning of the filter. Furthermore, because the pleats are in intimate contact, any contaminants that enter the filter become lodged within the inter-pleat space and are not fully removable. Therefore, the filter is not entirely cleanable and has a very limited reusable life. The filter also cannot be washed, brushed aggressively, or backwashed at high pressure because of its relative fragility. Therefore, the filter must be disposed of when it becomes contaminated.
Porex Porous Products Group, Fairburn, Ga. has improved upon the above filters by forming a molded filter element, preferably formed from a sintered porous plastic. The sintered porous plastic material used to form these filters provides a more durable composition and therefore permits the filter to be more effectively cleaned and reused over a longer period of time. For instance, the sintered porous plastic permits the filter to be repeatedly backwashed and cleaned. Backwashing is where a clean fluid is flown in a reverse direction from the normal direction of flow across a filter. The reverse flow dislodges particles that were previously trapped by the filter, thereby cleaning the filter for later use. Additionally, the sintered porous plastic is predominately uniform in composition and therefore the filter flow is not direction specific. A substance to be filtered can flow from the outside in as well as from the inside out.
Furthermore, because the sintered porous plastic filter is more rigid than the first type of filter described above, the Porex filters do not require a central core or an outer cage to provide a specific form and structure. The sintered porous plastic is capable of being formed into a shape and structure independent of employing a central core and outer cage. Moreover, molding permits the filter to be formed as a single piece, thus minimizing parts and simplifying manufacture as well as assembly.
Yet another benefit of the sintered porous plastic is that the pore size can be modified as desired. The pore size of the sintered material is dependent on the size and shape of the initial starting particles prior to sintering. Adjusting and determining the pore size based on the starting particle size and shape is described in U.S. Pat. No. 6,551,608 issued to Yao; U.S. Published Application No. U.S. 2003-0062311-A1; and U.S. Pending Application Ser. No. 09/375,383, each of which is incorporated herein by reference in its entirety.
It would therefore be desirable to form a filter that has a uniform surface for removing contaminants of multiple sizes, an increased filtering capacity, and an effective service life. It would further be desirable to form a filter having an increased capacity to capture contaminants and to form the filter so that it may be backwashed to clean off the contaminants so that the filter may be reused. Also, the surface preferably would be configured to retain the contaminants thereon, without creating dead spaces and blocking proper filter functioning.